Energy-based analysis of dynamic response and damage evolution of granite under incremental cyclic impact loading

Abstract

To investigate the mechanical response and damage evolution of surrounding rock subjected to repeated dynamic disturbances in deep underground engineering, cyclic impact tests on granite were conducted using a split Hopkinson pressure bar (SHPB) system under different incremental gas-pressure gradients, with constant-amplitude repeated impact tests performed for comparison. The results indicate that, under constant-amplitude repeated impact loading, the dynamic strength and dynamic elastic modulus generally decrease with increasing impact number, demonstrating a degradation process dominated by damage accumulation. Under incremental cyclic impact loading, the dynamic strength increases markedly with increasing impact amplitude; however, crack propagation during the later loading stage leads to stiffness degradation and sudden failure, reflecting competition among strain-rate strengthening, cyclic compaction, and damage-induced degradation. Energy analysis shows that the cumulative dissipated energy increases continuously with impact number. Under incremental cyclic impact loading, a larger impact-amplitude increment accelerates damage accumulation and causes the specimen to enter the high-damage regime at an earlier stage. The energy-based damage variable \(D\) effectively characterizes the damage evolution process and exhibits good agreement with the observed macroscopic failure characteristics. The results demonstrate that the impact-amplitude increment governs the rate and critical process by which granite transitions from compaction-induced strengthening to damage-dominated instability, while the stability of surrounding rock primarily depends on whether internal damage approaches the critical state of crack coalescence. These findings provide a theoretical basis for stability assessment of deep surrounding rock and the control of blasting-induced disturbances.